This invention generally relates to temperature control of electronics, and more particularly to a heat pipe configured for use in varying heat loads and environmental heat sink conditions. The invention will naturally limit heat rejection in low heat load and cold environment and resume its heat rejection capability in high heat loads and hot environment.
The reliability and lifetime of machines using electronic components, such as semiconductor devices for example, can be increased by reducing the temperature variations imposed on the electronic components during operation. As a result, electronic components commonly require a heat exchange device for cooling during normal operation. A heat pipe, for example, is one such heat exchanger and thermally connects an electronic component to the ambient environmental with minimal thermal resistance.
The elements of a heat pipe typically include a sealed pipe, a wick structure, and a small amount of working fluid which is in equilibrium with its own vapor. The length of the heat pipe is divided into three sections: an evaporator section, a transport (adiabatic) section, and a condenser section. Heat applied to the evaporator section by an external source is conducted through the pipe wall and wick structure where it vaporizes the working fluid. The resulting vapor pressure drives the vapor through the transport section to the condenser, where the vapor condenses, releasing its latent heat of vaporization to the provided heat sink through conduction, convection, or radiation. After rejecting the heat to the condenser, the capillary pressure created by menisci in the wick pumps the liquid phase working fluid back to the evaporator section.
During cold environment operation, such as at temperatures below the freezing point of the working fluid, the working fluid may freeze inside the condenser section of the heat pipe. Over time, the working fluid may become depleted from the heat pipe evaporator rendering the standard heat pipe nonfunctional.
Even with the frozen standard heat pipe, the first heat source is prevented from dropping to an undesirable temperature; however when the heat load to the heat pipe resumes, the heat pipe will not be able to transport the heat away from the first heat source and the heat load will rise to an undesirable high temperature.